1. Free and total activities of β-glucosidase, β-galactosidase, N-acetyl-β-glucosaminidase and β-glucuronidase have been determined fluorimetrically in five subcellular fractions of rat kidney. 2. The β-glucosidase activity appeared in the soluble fraction, β-glucuronidase had the distribution pattern of a lysosomal enzyme, and both β-galactosidase and N-acetyl-β-glucosaminidase had bimodal distributions. 3. Two types of β-galactosidase activity were found: a sedimentable type, having optimum pH3·7, mol.wt. about 80000 and slow electrophoretic mobility at pH7·0 in starch gel; and a soluble type of much faster mobility, having optimum pH5·5–6·5 and mol.wt. about 40000. 4. Evidence is presented that the β-glucosidase and the soluble type of β-galactosidase are the same enzyme. 5. Most of the N-acetyl-β-glucosaminidase activity was in the lysosome-rich fractions, but a significant proportion occurred in the microsomal fraction in a non-latent form. 6. The use of β-galactosidase and N-acetyl-β-glucosaminidase as lysosomal marker enzymes is complicated by the possible presence of multiple forms, but this limitation does not apply to β-glucuronidase in the rat kidney.
